Formula 1's young driver test will not be extended in to a fourth day for extra tyre running, the FIA has announced.

As AUTOSPORT predicted last week, the FIA has decided to keep the Silverstone test to its original July 17-19 dates despite extra tyre running required.

The decision all but dashes hopes that Mercedes had of winning a reprieve to be able to test Pirelli's new tyres before the next race in Hungary.

Pirelli is bringing extra sets of its new tyres - which will be the 2012 construction with the 2013 hard, medium and soft compounds - so teams can get an understanding of how they work on their current cars.

Race drivers are allowed to take part for one of the three days, but the FIA has reminded teams that they can only work on tyre testing.

It has specified that any car set-up changes that are made must be related to work for Pirelli and not done to improve the car.

A statement issued by the FIA said: "The test will now allow teams to field drivers who have competed in more than two F1 world championship events provided that the purpose of them doing this is to test tyres for Pirelli.

"In order to meet this requirement, all teams shall ensure that any changes made to a car at these times are exclusively related to the tyre tests set out in the run plan provided by Pirelli."

Pirelli motorsport director Paul Hembery has told AUTOSPORT that testing plans for the race drivers will be dictated by his engineers, and not the teams.

"The teams will have a very clear tyre test programme," he said. "They have to run what we are telling them to run."